[Sema] Remove unused variable 'FromExtType' [NFC]

Last use of the variable was removed in a29afb7
 [HLSL] Allow truncation to scalar (#104844)

gcc warned about this:
  ../../clang/lib/Sema/SemaOverload.cpp:2070:15: warning: unused variable 'FromExtType' [-Wunused-variable]
  2070 |     if (auto *FromExtType = FromType->getAs<ExtVectorType>()) {
       |               ^~~~~~~~~~~

Author: mikaelholmen

clang/lib/Sema/SemaOverload.cpp

@@ -2067,7 +2067,7 @@ static bool IsVectorConversion(Sema &S, QualType FromType, QualType ToType,
 
   // There are no conversions between extended vector types, only identity.
   if (auto *ToExtType = ToType->getAs<ExtVectorType>()) {
-    if (auto *FromExtType = FromType->getAs<ExtVectorType>()) {
+    if (FromType->getAs<ExtVectorType>()) {
       // There are no conversions between extended vector types other than the
       // identity conversion.
       return false;